My recent rebuild is mechanically running well, but there is a decently loud hissing type noise that you can hear when you hit the gas and put things under load. It goes away if I am barely touching the gas and driving on level road, or idling. Its loud enough that I can hear it very well inside the car, and echoing off the houses as I drive down the street. From what I can tell, it is coming from the exhaust side of the engine, near the BAC and idle air control. I've checked and checked again for hoses leaking, but it seems like a hose leak wouldn't be quite this noisy (I may be wrong). I'd appreciate any suggestions to fix this problem, whether it be a major or minor issue. Thanks.

 

Exhaust leak check manifold to engine gasket or down pipe to manifold gasket

 

Makes sense, I'll check it out and see if there's an issue. Thanks.